Process of making titanium containing pigments



4 Aug. 10, 1943. A, T, McCORD v 2,326,156

PROCESS OF MAKING TITANIUM CONTAINING PIGMENTS Filed Aug. 1, 1940 X-RAYDIFFRACTION PATTERNS SCALE SCALE AU ANATASE RUTILE A-TITANIC ACID AU 606.0

-INVENTOR Andrew Z'MZ'ord BY Q W llai.

ATTORNEYS Patented Aug. 10, 1943 PROCESS OF TITANIUM CONTAINING PIGMENTSAndrew T. McCord, Collingswood, N. J., assignor to The Sherwin-WilliamsCompany, a corporation of Ohio Application August 1, 1940, Serial No.349,345

11 Claims. ((1106-3110) This invention relates to titanium pigments ofthe type comprising titanium oxide and a socalled extender, and whichare useful in paint and other liquid coating compositions and forvarious other purposes.

Heretofore it has been the practice to use a solution of titaniumsulfate in sulfuric acid, and which has been obtained by the treatmentof ilmem'te or other titaniferous ores with sulfuric acid, and toprecipitate thetitanium as titania hydrate by thermal hydrolysis in thepresence of the extender by boiling. The mixture of the extender andsuch hydrate is then calcined to drive off the sulfuric radical andconvert the hydrate into pigmentary titanium oxide.

My improved product possesses a substantially greater tinting strengthand hiding power for a given titanium oxide content than have othercomposite titanium oxide pigments heretofore available to the'trade andhaving the same percentage of titanium oxide. It is also less sensitiveto water, has superior brightness and resistance to chalking in paintfilms on exterior exposures, and greater film strength.

My improved process for making the pigment involves certain novel andimportant steps.

As an important novel feature of my improved pigment, the titanium oxideconstituent has a rutile crystalline structure instead of thecrystalline structure of anatase, and as an important feature of theprocess thepigment is formed from the extender and a certain form oftitanium hydrate, both in solid form, .in an acidified slurry which isheated to convert the titanium hydrate to the desired crystalline formand from which the solids in intimately mixed, very finely divided form,may be readily separated and thereafter calcined. v

The titania hydrate which I employ differs in crystalline structure fromhydrates produced by the sulfuric acid process and by various otherprocesses commercially used or known in the art. It is characterized byproducing upon X-ray analysis, a band pattern, the bands correspondingin position to neither those of rutile nor those of anatase. It isdistinguished from the band pattern of the hydrate produced by thesulfate process and obtained by thermal hydrolysis of a sulfatesolution, wherein the bands correspond in position to the characteristicanatase lines, and is also distinguished from the band pattern producedby thermal hydrolysis of nitrate or chloride solution wherein the bandscorrespond in osi. tion to the characteristic rutile lines.

The titania hydrate which I employ may be converted into substantiallypure rutile in pigmentary condition by calcination. I will hereinafterdesignate such form of titania hydrate or titanic acid by thearbitrarily selected letter 7 as a prefix to distinguish it from otherforms of titania hydrate or titanic acid which do not have the samecharacteristic properties.

In the accompanying drawing I have illus trated the position of thebands of this 7 titanic acid, as well as the positions of thecharacteristic rutile and characteristic anatase difiraction lino-s. Itis to be understood that the X-ray difiraction pattern of all hydratesappears as bands, rather than as sharp lines such as are obtained fromthe calcined pigment wherein crystallization is fully developed. In thediagram itwill be noted that the bands of the 'y titania hydrate do notcor respond to the atomic planes of the lines for the two crystallinemodifications of TiOz as set forth in Weiser and Milligan, Journal ofPhysical Chemistry, April, 1934, page 517. The positions are as follows:

1322 7 Lines of Lines of hydrate anatase rutile A. U. A. v. A. U. 5. 833. 49 3. 24 3. 99 2. 37 2. 48 3.145 1. 883 2. 29 2. 600 1. 695 2. 18 2.132 1. 655 2. 04 1. 888 1. 477 1. 635 1. 499 1. 358 1. 617 l. 354 1.334 1. 479 1.177 1. 261 1. 448 956 1. 161 1. 351 868 1. 044 1. 240743 1. 015 1. 167

This v titania hydrate may be obtained in' various ways, but preferablyfrom a solution of titanium-ammonium fluoride, a complextitamum-ammonium fluoride, or titanium tetrafluoride com ound, which"has been treated with ammonia.

A suitable ammonium fluotitanate in crystalline form maybe obtained bycrystallization of the titania liquor produced by a fluorine processsuch as described in the Kliefoth Patent 2,174,920.

The titania liquor obtained by attack of ilmenite or other titaniferousores with a suitable fluorine compound, as described by Kliefoth, issubjected to crystallization, whereby substantially pure ammoniumfiuotitanate in crystalline form is obtained and separated from theexcess of ammonium fluoride, NHeF, and other impurities as iron or othermetal impurities.

Merely as examples of a few Ways in which lowing composition:

Pounds Percentage After minutes the slurry is filtered and the .r

cake or precipitated titania hydrate is washed with. 2% pounds of water.The cake may be re-slurri d with 250 pounds or" water, boiled for onehour, filtered, and washed with 250 pounds of boiling water. The wetcake weighing about 250 pounds be dried at 110 I1, and the weightreduced to 55.6 pounds. The dry cake on analysis shows:

Per cent T102 90 N11; 4.5

F 0.1 H2O 5.5

Example 2.-l pounds of titanium tetrafluoride solutiofi containing 14.5%T102 and 14% F is mixed with 500 pounds of 30% aqueous ammonia. Themixture is agitated for one hour, then filtered and washed with hotwater.

Example 3.50 pounds of slightly soluble Ti(OH)2F2.2NH4F is ball milledfor five hours with 200 pounds of 20% aqueous ammonia. The slurry isthen filtered and the residue washed with boiling Water to reduce thefluorine content to about 0.05%.

Example 4.I may use a titanium-ammomum fluoride solution made accordingto the Svendsen Patent No. 2,042,435 and containing of T102. and a ratioof about 12 mols of F to 1 of T102.

Such a solution may contain:

. Per cent T102 5 F 14.28

N'Hs 8.52

1000 pounds of Such solution, and containing 50 pounds T102 is slowlyadded to 1500 pounds of aqueous ammonia over a period of 40 minuteswhile the temperature is maintained below 40 C. The precipiated hydratemay be 111- tered and washed, then re-slurried at 100 C. for one hour,and again separated from the liquid.

- The cake may be dried at 100 C. to yield 56 pounds of dry cake.

The foregoing are merely examples of ways in which one may prepare atitania hydrate suitable for use in making my improved extended pigment.

I preferably employ calcium sulfate as the extender because of its wellknown desirable propcrties, which have been takenv advantage of intitanium pigments for many years (see Barton Patent No. 1,155,462), butin my improved product a wide variety or" other extenders may beemployed in finely divided or powdered form, such as natural gypsum,natural or artificial anhydrite, natural or artificial barium sulfate,asbestine, micas, pinites, silica, etc, or mixtures of these extenders.

I do not desire to be limited to any specific proportions of extenderand rutile, but for comreasons, in view of the difference in cost or theextender and the titanium oxide, and the fact that the hiding power ofmost commercial extended titanium pigments is somewhat greater that ofthe same amount of titanium oxide without extender, it has been commonto about 70% of extender and about 30% of ti-= in oxide in making anextended titanium 1 proportions of extender and titanium snide, andhaving the titanium presei t in the crystalline form of rutiie, shows atinting strength of 575 350 when tested according to A. S. T. M.Designation D 332-36, as compared to 450 to 470 the previously employedpigments er the same percentage composition of calcium sulfate andtitanium oxide. The corresponding hiding power for one pound of myimproved pigment in linseed oil is 55 to 65 square feet of blacksurface, when tested. according to S. T. M. Designation L- -39, ascompared with 48 square feet for the prior pigments. These standardmethods of test given in A. S. T. M. Standards, 1939, part II,Non-metallic materials-constmctionah which publication also gives A. S.T. M. Designation'D d75-39. Standard specifications for titanium dioxidepigments.

As an example of my improved process, and by which my improved productmay be made, one

' may proceed as follows:

Pounds Extender 117 H2SO4 57.2 H2O 324.5

To this amount of acidulated slurry there is added 55.6 pounds of thedry, finely ground 7 titania hydrate which, instead of containing aquantity (5 to 9%Q of S03 radical, as in the case of hydrate prepared bythe sulfuric process, contains a small amount of ammonia. and is analkaline type of hydrate instead of an acid type.

The analysis of the mixture in the foregoing example is:

Pounds Percentage The ammonium sulfate (NI-102804 is formed bycombination of the ammonia in the hydrate, and some of the sulfuric acidof the slurry. So far as known, this takes no part in the reaction. Themixture may be ball milled to insure smoothness of the slurry and heatedwith agitation to boiling. The boiling is continued for about two hours.curs without any substantial solution.

The exact nature of the transformation which is effected by this boilingin the presence "of sulfuric acid and the extender is one which changesthe hydrate to a form having a band pattern similar to but weaker thanthat of the hydrate produced by the sulfate process, but the twohydrates differ radically in that the transformed titania hydrate oncalcination gives rutile, and the hydrate of the sulfate process oncalcination gives anatase.

As another example, the mixed slurry to be heated may be made by adding250 pounds of wet hydrate cake containing hydrate equivalent to 50 Apounds of titanium oxide, 117 pounds of CaSO4,

140 pounds of water, and 61.0 pounds of 66 B. H2504, and ball millingthe mixture, rather than adding the dry hydrate to the slurry ofextender.

The hot slurry is then filtered and the residual cake washed with 400pounds of cold water. The washed cake may be dried prior to calcination,or may be calcined directly, or may be treated prior to calcination withvarious additional agents, the calcination being for about five hours atabout 975 C. As the ratio of the extender to the titanium oxide was117:50, and the other ingredients are drawn off in drying and calcining,

the ratio of the two ingredients of the resulting pigment will be 70:30.

As another example giving the same 70:30 ratio, a mixture of 77.7 gramsof 'y titanic acid. dry, containing 60 grams of T102, 140 grams of drycalcium sulfate, and 380 grams of water, may be mixed to a uniformslurry, and 73.57 grams of 93.2% H2804 (equivalent to 69.55 grams H2304)added. The slurry possesses the following composition:

. Per cent TiOz 8.950 (run) 2so4 1.720 F .010 H2O 59.550 Hzsm 8.950CaSOr 20.82

The mixture should be boiled for 2 hours with good agitation, dewatered,for instance by the During this period transformation ocuse of a vacuumfilter, and washed to remove mother liquor, and the resulting cakecalcined for 4 hours at 975 C. The composite pigment resulting gives atinting strength of 620, and a brilliant white color.

The amounts of materials employed, the concentrations of the solutions,the solid .contents of the slurries, the time of heating, boiling,calcining, etc., the number of washings, and other factors as abovegiven are those which have been found satisfactory in use, but except asindicated, they are not critical, and obviously could be varied in manyparticulars and through a wide range, to produce the 30:70 ratio ofrutile and extender in the product. The various factors may also bevaried to produce any other ratio of rutile to extender, such as 10:90,20:80, 40:60, etc.

The temperature at which the mixture is calcined is about 950 C. to 9750., but a temperature up to 1000 C. or even 1050 C. does not cause anysubstantial change in the color, hiding power or tinting strength. At1200 C. or even 1300 C., the color is lowered to only a slight extent,and is far better than is obtained if anatase be employed instead ofrutile.

The acidity of the slurry is given above as 1.0 pound of H2804 for eachpound of titanium oxide, but it may be only 0.5 or lower, or the ratiomay be even higher. The amount of H2804 should be less than 2.47 poundsfor each pound of TiOz, or less than 2 mols for 1 mol of and while theacid concentration should' not be sufliciently high to cause anysubstantial dissolving of the hydrate or converting of it to sulfate, itmust be sufficiently high to cause dispersion of the hydrate. 'Thisconcentration may be from 6 to 15% H2SO4 in the liquid, and should notvery substantially exceed that percentage. As the titanium compound isnot in solution in the slurry but only dispersed, the

recovery of titania is substantially of that added.

The use of ammonia for the treatment of the titanium fluorine compoundto produce the desired form of the hydrate is not essential, as otheralkalies may be used. Using X-ray diffraction pattern methods as a meansof identifying 7 titanic acid, it has been found that the solution oftitanium tetrafluoride with ammonia or sodium hydroxide; the compound Ti(OH) 2F2.3NH4F with ammonia; the compound Ti(OH)2F2.2NH4F with ammonia;titanium nitrate. in water or nitric acid solution with ammonia; andvarious other titanium compounds with any suitable alkali or equivalentbase may be employed. The best results seem to be obtained by the use ofan ammonium-titanium fluorine compound with ammonia.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is:

1. The process of making a titanium containing pigment, which includesthe steps of forming a slurry of an extender and a titania hydrate bothin solid form, in water containing a quantity of sulfuric acid inproportion of less than 2.47 H2804 to 1 part T102 by weight, saidhydrate showing on X-ray analysis the pattern characteristic of -titanicacid, boiling said slurry and separating the mixed solids from theacidified water.

2. The process of making a rutile containing pigment, which includes thesteps of forming a slurry of an extender and a titania hydrate both insolid, finely divided form, in water contain ing sulfuric acid inproportion by weight of less than 2.47 parts H2SO4 to 1 part fIiOz, saidhydrate showing on X-ray analysis the pattern characteristic of -titanicacid, boiling said slurry, separating the mixed solids from theacidified water, and calcining.

3. The process of making a titanium containing pigment, which includesthe steps of forming a slurry of an extender and a titania hydrate insolid, finely divided form, in water containing sulfuric acid inquantity less than 2 mols of H2804 to 1 mol of T102 said hydrate showingon X-ray analysis the pattern characteristic of 'y-titanic acid, boilingsaid slurry, separatingthe mixed solids from the acidified water,washing to remove residual acid, and calcining to corn vert the hydrateinto rutile in the presence of the extender.

4. The process of making a pigment composed essentially of an extenderand rutile, which includes the steps of forming a slurr of the extenderand a titania hydrate containing a small amount of alkali, in watercontaining an amount of acid more than sufiicient to neutralize thealkali but less than 2.47 parts by weight of H2804 to 1 part TiOz, saidhydrate showing on X-ray analysis the pattern characteristic of'y-titanic acid, boiling the slurry, and thereafter separating the mixedsolids from the acidified water.

5. The process of making a pigment composed essentially of an extenderand rutile, which includes the steps of forming a slurry of the extenderand a titania hydrate containing a small amount of alkali, in watercontaining an amount of acid, the ratio of acid to titanium oxide byweight being substantially less than 2.47:1, said hydrate showing onX-ray analysis the pattern characteristic of 'y-titanic acid, boilingthe slurry, and thereafter separating the mixed solids from theacidified water.

6. The process of making a pigment composed of an extender and rutile,which includes forming a slurry of -titanic acid containing a smallamount of ammonia, calcium sulfate, water and an amount of sulfuric acidsubstantially equal in weight to that of the titania of said -titanicacid, boiling the slurry for about 2 hours with agitation, dewatering ona vacuum filter, washing to remove mother liquor, and calcining thefilter cake for about 4 hours at about 975 C.

7. The method of forming a pigment comprising rutile and an extender,which includes forming a slurry of calcium sulfate and a titania hydrateformed by precipitation of an ammonium titanium fluoride compound withammonia, and containing a small amount of alkali, said slurry beingformed in water containing sulfuric acid, the ratio of H2804 to titaniumoxide by weight being about 1:1, and more than sufficient to neutralizesaid alkali, boiling the slurry, separating the mixed solids in finelydivided condition from the acidified water, and calcining the solids toconvert the titania hydrate into rutile, in the presence of theextender.

8. The process of forming a pigment, which ineludes treating a titaniumfluorine compound with an alkali to form a compound composed essentiallyof titanium, hydrogen and oxygen and having a crystal structurecharacterized by exhibiting upon X-ray analysis a difiraction patterncomposed of bands spaced at substantially the following positions on ascale calibrated in Angstrom units: 5.83, 3.99, 3.145, 2.600, 2.132,1.888, 1.499, 1.354, 1.177, .956, .868, .743, forming a slurry of saidhydrous titanium oxide and an extender in water acidified with sulfuricacid, the ratio of H2804 to 'I'iOz by weight being less than 2.47:1,boiling the slurry, separating the finely subdivided solids from theacidified water, and calcining to convert the hydrous titanium oxideinto rutile in the presence of the extender.

.9. In the preparation of an extended pigment, the steps of adding anaqueous solution of a complex ammonium titanium fluoride compound to anexcess of aqua ammonia, separating the precipitated titania hydrate,forming a slurry of said hydrate and an extender in water containing aquantity of sulfuric acid less than 2.47 parts by weight of H2So4 to 1part 'IiOz, boiling the slurry, and thereafter separating the finelydivided mixed hydrate and extender in finely divided solid form.

10. The process of making a pigment composed essentially of rutile andan extender, which in cludes the steps of forming an aqueous solutior ofammonia fiuotitanate, contacting said solution with an excess of aquaammonia, separating, washing and boiling the resulting titania hydrate,forming a slurry of said hydrate and the extender in water containing anamount of sulfuric acid not in excess of 2.47 parts per part of TiOz byweight, boiling, separating the mixed extender and titania hydrate,washing, and calcining at 800 C, to 1200 C.

11. The process of making a pigment composed essentially of rutile andan extender, which includes the steps of forming an aqueous solutionofammonia fiuotitanate, contacting said solution with an excess of aquaammonia, separating, boiling and washing the resulting titania hydrate,forming a slurry of said hydrate and the extender in water containing anamount of sulfuric acid not in excess of 2.47 parts per part of TiO2 byweight, boiling, separating the mixed extender and titanium hydrate,washing, and

calcining at 950 C. to 975 C.

ANDREW T. MCCORD.

